1. Field of the Invention
The present invention relates to an integrated circuit package.
2. Background Information
Integrated circuits are typically assembled into packages that are soldered to a printed circuit board. Each integrated circuit may be connected to a substrate of the package with a number of solder bumps in a process commonly referred to as controlled collapsed chip connection (C4).
During operation, the integrated circuit generates heat which raises the temperature of the package. Additionally, the package temperature may be increased during assembly of the package. The increase in package temperature will cause the integrated circuit and the substrate to expand. The substrate is typically constructed as a composite of metal and organic material which have a different coefficient of thermal expansion than the silicon material of the integrated circuit. The mismatch of thermal expansion coefficients may create stresses in the solder bumps when the package is thermally cycled. The stresses may create cracks and electrical opens in the package.
To improve the structural integrity of the solder bumps an epoxy can be dispensed into the integrated circuit/substrate interface. Even with the epoxy underfill it has been found that the substrate may delaminate and crack when the package is thermally cycled. It would be desirable to provide a substrate for a C4 integrated circuit package which has a coefficient of thermal expansion that matches the coefficient of thermal expansion of the integrated circuit.
During operation the integrated circuit generates heat which must be removed from the package to maintain the circuit junction temperatures below a threshold value(s). Heat slugs and heat spreaders are sometimes incorporated into the package to facilitate the removal of heat from the integrated circuit. Heat slugs and heat spreaders may not be adequate to effectively remove all of the heat from a high powered integrated circuit such as a microprocessor. Some of the heat may transfer through the package substrate and into the printed circuit board. Organic substrates of the prior art have a relatively low coefficient of thermal conductivity. It would be desirable to provide a substrate which has both a coefficient of thermal conductivity that is higher than organic substrates of the prior art and have a coefficient of thermal expansion that matches the integrated circuit.